1. Field of the Invention
The present invention relates to a nitride semiconductor light-emitting device and a method for producing the nitride semiconductor light-emitting device.
2. Description of the Related Art
A nitride semiconductor light-emitting device emits light having a wavelength extending from the ultraviolet to the infrared region. When the nitride semiconductor light-emitting device includes an InGaN layer as an active layer, the wavelength in the visible region can be controlled by changing the mixed crystal ratio in the InGaN layer. A blue LED can be combined with a yellow fluorescent material to create a white light source, which has been widely used in display devices and lighting devices. Examples of known acceptor dopants for nitride semiconductors include Be, Mg, and C. Among these elements, Mg is often used as a p-type conductivity dopant because Mg allows a high p-type conductivity to be realized. However, use of Mg causes a problem called “memory effect”, which is a phenomenon caused by Mg attached to a reactor member when a Mg-containing raw material was used in the reactor desorbing from the reactor member as it grows and being unintentionally mixed in a crystal. Mixing of Mg in an active layer increases the occurrence of non-radiative recombination, which results in a reduction in luminous efficiency.
Therefore, it is very important to suppress the memory effect and prevent the unintentional doping in the active layer. Mg is discussed above as an example, and other raw materials that can be used for acceptor dopants in GaAs, such as Zn, Se, and Te, have also the problem of memory effect. Hitherto, several methods for addressing the memory effect have been proposed. For example, Japanese Patent No. 3603598 proposes a method for producing a III-V group compound semiconductor light-emitting device. In this method, a semiconductor layer is formed in a reactor in which a Mg-containing raw material is not used and subsequently a p-type semiconductor layer is formed in another reactor in which a Mg-containing raw material is used, and thereby the memory effect is suppressed. Examples of other known methods include a method of cleaning a reactor in which a Mg-containing raw material has been used every time after the growth in order to remove Mg; and a method of growing a thick semiconductor layer that allows Mg to be incorporated thereinto in order to prevent Mg from being mixed in an active layer.
However, these existing methods for manufacturing a nitride semiconductor have the following problems. The method described in Japanese Patent No. 3603598, in which a semiconductor layer is formed in a reactor in which a Mg-containing raw material is not used and subsequently a p-type semiconductor layer is formed in another reactor in which a Mg-containing raw material is used in order to address the memory effect, incurs high cost because two or more reactors need to be prepared. All the other methods described above also incur high cost due to addition of the cleaning step, an increased amount of raw material used, an increased manufacturing time, and the like. These problems occur not only in the case where a nitride semiconductor is used but also in the case where other material systems are used for a semiconductor.